Gb	Eng
讲课时不要岔开（主题）.	Don't digress (from the subject) when lecturing.
上课时不准戴帽子。	Don't keep your hat on in class.
他因在上课时吸烟而被开除了。	He was expelled for smoking in class.
他很困倦，上课时候都睡着了。	He was so sleepy that he fell asleep during the class.